Grinding machine

ABSTRACT

THIS INVENTION RELATES TO A GRINDING MACHINE AND, MORE PARTICULARLY, TO APPARATUS ARRANGED TO GENERATE A SURFACE OF REVOLUTION BY THE ABRASIVE METHOD.

March 16, 1971 UHTENWQLDT ET AL 3,57%,185

GRINDING MACHINE 4 Sheets-Sheet 1 Original Filed April 9, 1965HERBERT/P. UHTENWOLDT FREDERICK A. HOHLER ROBERT 6. HATSTAT INVENTORSMarch 16,1971 H, R HTENWOLDT ET AL 3,570,185

GRINDING MACHINE 4 Sheets-Sheet fl Original Filed April 9, 1965 m GRMarch 16, 1971 H. R. UHTENWOLDT ET AL 3,570,185

GRINDING MACHINE Original Filed April 9, 1965 4 Sheets-Sheet FIG.

March 16, 1971 UHTENWQLDT ET AL 3,570,185

GRINDING MACHINE 4 Sheets-Sheet 4.

Original Filed April 9, 1965 United States Patent Ofice US. Cl. 51-37 3Claims ABSTRACT OF THE DISCLOSURE This invention relates to a grindingmachine and, more particularly, to apparatus arranged to generate asurface of revolution by the abrasive method.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of my application Ser. No. 759,811, filed Sept. 9,1968 which, in turn, was a continuation of my application Ser. No.451,712, filed Apr. 29, 1965 now abandoned.

BACKGROUND OF THE INVENTION In the grinding of workpieces, it isadvantageous to feed the rotating abrasive wheel into the material ofthe Workpiece with the greatest possible force commensurate with thestrength of the wheel and the finish desired in the workpiece surface.In accordance with the controlled force method of operation, the wheelis fed into the material at a pre-determined level of force, the actualgeometric movement (feed rate) between the workhead and the wheelhead ofthe grinding machine taking place in an uncontrolled manner. Suchoperation results in several definite advantages in speed of stockremoval and in adequacy of the quality of the finish of the workpiece.In the past, however, some difficulty has been experienced with thismethod of grinding because of vibration and uneven movement of the wheeltoward the workpiece. There is some reason to believe that this is dueto the friction-free character of the sliding surfaces arranged topermit relative movement between the wheelhead and the workhead. Also,as the wheel becomes smaller in diameter, there is a tendency for it toout faster; this upsets the carefully selected grinding parameters andaffects the quality of the work. These and other difiicultiesexperienced with the prior art devices have been obviated in a novelmanner by the present invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine using the controlled force method of grinding, whichmachine is free of erratic movement of the wheel toward the workpiece.

Another object of this invention is the provision of a grinding machineprovided with a low friction sliding movement between the wheelhead andthe workhead wherein vibration or skipping movement between the surfacesis not permitted.

A further object of the present invention is the provision of acontrolled force grinding machine which is free of a tendency to producevibratory movement between the elements.

It is another object of the instant invention to provide a grindingmachine having a hydraulic system for producing controlled forceoperation with a reduced tendency for undesirable movement between theelements.

Another object of the invention is the provision of a. grinding machineusing the controlled force process,

Patented Mar. 16, 1971 wherein reduction of wheel diameter does notaffect the quality of the work.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION In general, the invention consists of agrinding machine having a base, a workpiece support mounted on the base,a wheelhead support mounted on the base, and a hydraulic actuator havinga piston movable within the actuator bringing about relative feeding andretraction movement between the workpiece support and the wheelheadsupport. Means is provided for presenting an incompressible fluid to theactuator at one side of the piston at a con trolled pressure duringfeeding movement. The actuator consists of a cylinder having a head atthe said other side, the head being provided with a passage. A damperrod lies in the passage and is accessible from the exterior of themachine to permit regulation of the relative positions of the rod andpassage and, therefore, regulation of the restriction to flow of fluidpresented thereby. Means is also provided connected to the actuator atthe other side of the piston to permit excape of fluid at a restrictedselected rate during feeding movement and alternatively to present afixed pressure fluid during the retraction movement. Separate sourcesare provided from which originate the controlled pressure fluid and thefixed pressure fluid.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention,however, may be best understood by reference to one of its structuralforms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a perspective view of a grinding machine embodying theprinciples of the present invention,

FIG. 2 is a sectional view of the apparatus taken on the line II-II ofFIG. 1,

FIG. 3 is a sectional View taken on the line III-III of FIG. 2,

FIG. 4 is a schematic diagram of hydraulic apparatus used in theinvention,

FIG. 5 is an enlarged view of a portion of the apparatus,

FIGS. 6 and 7 are schematic views of the elements of the grindingmachine, and

FIG. 8 is a graphic representation of force-rate relationships.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, itcan be seen that the grinding machine, indicated generally by thereference numeral 10, is of the type shown and described in the patentof Hohler et al., No. 3,197,921 which issued on Aug. 3, 1965. It isprovided with a lower base A on which is mounted a workhead 14 and awheelhead 13. Around the front of the base extends a splash guard Bwhich is readily removable. Extending upwardly from the rear of the baseA is a superstructure C having two arms similar to the arm D whichextend forwardly from the ends of the base. Mounted between the arms isa control cabinet B. At one end of the machine is located a coolant tankF receiving coolant returned from the machine through a pipe G.

Referring next to FIGS. 2 and 3, it can be seen that the grindingmachine 10 also has a base 111 on which is mounted a wheelhead table 12.carrying the wheelhead 13. The base 11 also carries the workhead 14which has shoes \15 for supporting and rotating a workpiece 16. Theworkpiece is shown, for the purposes of illustration, as a ball bearingrace having an internal surface of revolution, such as a bore 17 whosesurface is to be finished.

The wheel head 13 carries a rotatable spindle 18 on which is mounted anabrasive wheel '19, means being provided to rotate the spindle andwheel. The base 11 carries a piston 21 slidable in a longitudinal bore22, those elements serving to define a FEED cylinder 23.

Referring next to FIG. 4, which shows the hydraulic apparatus, thegrinding machine is provided, as has been stated, with a table cylinderwhich operates to move the workhead -14 axially toward and away from thewheel 19, a TABLE IN dashpot 24, a loading cylinder 25 (which serves toload and unload workpieces from the machine) and, of course, the feedcylinder 23, which has been described. The machine is also provided witha compensation cylinder 26, which is connected to a compensatingarrangement (not shown) and to the base 11 in such a way as tocompensate for removal of stock from the abrasive wheel 19 duringdressing by a diamond. The machine is also provided with a WHEELHEADSWIVEL cylinder 27 and with GAGE-IN cylinders 28 and 29. The machine isalso provided with DIAMOND TURNER cylinders 31 and 32 serving to rotateand to advance the dressing diamond from time to time. It should benoted that the hydraulic circuitry is shown, in accordance with theJ.I.C. Standards for industrial equipment. Pressure hydraulic fluid isfurnished by a pump 33 driven by an electric motor 34. From the pumpextends a 500 p.s.i. unfiltered line 35. Another ouput of the pump isconnected to a filter 36 from which extends a line 37 and a line 38. Theline 38 is at 500 p.s.i. filtered, while the line 37 operates through apressure-reducing valve 39 from which extends a line 41 carryinghydraulic fluid at approximately 125 p.s.i. Extending through thecircuitry is a drain line 42 which returns all fluid to the sump.

The line is connected through a check valve 43 to the table cylinder 20,while the other side of the cylinder is connected by a line 44 to thedrain line 42 through a manual shut-off valve 45. The same side of thecylinder 20 which is connected to the line 44 is also joined to a line46 which is joined to a solenoid valve 47, the other side of which isconnected by a line 48 to a flow control valve 49, the other side ofwhich is attached by a line 51 to a TABLE INDEX valve 52.

Also connected to the TABLE INDEX solenoid valve 52 is a line 53 leadingto a TABLE OUT dashpot 54 whose hydraulic side is connected in a closedcircuit through a flow control valve 55. The other side of the dashpot54 is attached by a line 56 to the drain line 42. Extending through thehydraulic circuitry is a 5 p.s.i. line which is joined through a checkvalve 57 to the drain line 42. The TABLE INDEX valve 52 is attached by aline 58 to the line 35 and the valve is also connected by a line 59 tothe 5 p.s.i. line 60. The line 46 is connected around the cylinder 20 tothe line 35 by a line 61 containing a throttle 62. The same end of thecylinder 20 that is joined to the lines 44 and -46 is also attached by aline 63 to the TABLE IN dashpot 24. Connected to the end of the dashpotin the usual way is a check-valve 64 and a throttle 65. The 500 p.s.i.filtered line 38 is joined by a line 66 to table hydrostatic controlpockets 67 which drain through a line '68 into the drain line 42.

The 500 p.s.i. line 38 is joined by a line 70 to a load valve 69 which,in turn, is connected by a line 71 to one side of the load cylinder 25.The other side of the cylinder is connected through a valve 73 by a line74 back to the valve 69 whose drain side is joined by a line 75 to the 5psi. line 60. The 125 p.s.i. line 41 is attached by a line 76 to theCROSS-SLIDE COMPENSATION valve 77, the other side of which is joined bya line 78 to the COMPENSATING cylinder 26. The other side of theCOMPENSATING cylinder is connected by a line 79 to the valve 77 whosedrain side is connected by a line 80 to the 5 p.s.i. line 60.

The 500 p.s.i. line 38 is connected by a line 81 to a LOW-FORCE pressureregulating valve 82 and also to a HIGH-FORCE pressure regulating valve83. The output side of the valve 82 is joined by a line 84 through valve94 to the CROSS-SLIDE valve 85, while the valve 83 is similarlyconnected to a valve 85 by a line 86'. The valve '85 is joined by a line87 to the CROSS-SLIDE FEED valve 88, the other side of which isconnected by a line 89 to the 5 p.s.i. line 60. The line 87 is alsoconnected by a line 92 to the FEED cylinder 23. The 125 p.s.i. line 41is connected to a backotf high pressure valve 96, the other side ofwhich is connected by a line 97 to a backoff valve 98, the other side ofwhich is connected to a line 101. The line 101 is connected to across-slide damper 102, the other side of which is connected to a line103. The line 92 is connected to the outer end of the cylinder 23, whilethe line 103 is connected to one end of the FEED cylinder 23.

The 500 p.s.i. line 38 is connected by a line 104 to a backoffpressure-regulating valve 105 whose output is connected by a line 106 tothe drain line 42 through a backoff pressure orifice 107. Between theorifice 107 and the valve 105 is connected a line 108 leading through acheckvalve 110 to the line 97.

The 500 p.s.i. line 38 is also joined by a line 111 directly to aCOMPENSATION SLIDE PRE-LOAD cylinder 112. The 500 p.s.i. line 38 is alsojoined by a line to a damper bypass valve 113 whose output is joined bya line 1114 through the hydraulic control end of the damper 102. Theline 38 is also joined by a line #115 to the cross-slide hydrostaticcontrol pockets 116. These pockets are joined by a line 117 to the drainline 42. The line 117 also receives fiuid arriving in a line 118originating in the ends of the FEED cylinder 23 and carrying leakage andfrom a throttle line 119 originating in the end of the cylinder 23 towhich the line 92 is attached. The 500 p.s.i. line 38 is joined by aline 121 to the WI-IEELHEAD SWIVEL valve 122 which in turn, is joined bya line 123 to the WHEELHEAD SW-IVEL cylinder 27. The other side of theWHEELHEAD SWIVEL cylinder is connected by a line 124 back to the valve122 whose drain side is connected by a line 125 to the 5 p.s.i. line 60.The 500 p.s.i. line 38 is connected by a line 126' to a SINGLE-J ET GAGEvalve 127 which, in turn, is connected by a line .128 to the GAGE INcylinder 28. The other side of the cylinder 28 is connected back to thevalve 127 whose drain is joined by a line 131 to the 5 p.s.i. line 60.The 500 p.s.i. line 38 is attached by a line 132 to a DOUBLE-JET GAGEvalve 133, the other side of which is connected by a line 134 to theGAGE IN cylinder 29. The other side of the cylinder 29 is joined by aline 135 directly to the drain line 42 and the drain side of thesolenoid valve 133 is also joined by a line 136 to the drain line 42.

The 500 p.s.i. line 38 is attached by a line 137 to a DIAMOND TURNERValve 138, the other side of which is joined by a line 139 to theDIAMOND TURNER cylinders 31 and 32. The other side of the cylinder 31 isjoined by a line 141 back to the valve 138 whose drain is attached by aline 142 to the 5 p.s.i. line 60.

Returning now to FIGS. 2 and 3, it can be seen that the base 11 isprovided with three spaced vertical abutments 143, 144, and and that thepiston 21 is fixedly mounted in them and extends horizontally throughthem. The piston 21 has an enlarged central portion and two reduced endportions, the end portions being mounted in the abutments 143 and 145and the enlarged portion extending through the abutment 144. The endthat appears in the left in FIG. 2 would normally be at the rear of thegrinding machine and resides in an abutment 146 which extends downwardlyfrom the lower surface of the wheelhead table 12. The abutment 146 isprovided with a portion of the bore 22 and a head 147 overlying thebore. Extending through the head and into the bore is the line 92. Theother end of the piston 21 resides in an abutment 148 which extendsdownwardly from the table 12, this abutment being provided with anotherportion of the bore 22 and also being provided with a head 149.Extending into the head are a line 103 and a line 151, the latterincluding a throttle 152. Extending downwardly from the front of thetable 12 is an apron 153. Carried by the apron is a throttle rod 154which extends into the head 149. As is evident in FIG. 4, the headcarries a bore 155 and the rod is provided with a portion 156 which fitsthis bore exactly. Next to the portion 156 is a reduced portion 157,while the extreme end of the rod carries an enlarged portion 158, theenlarged portion 158 being not quite as large as the bore 155, however.It will be understood, of course, that the portions shown in the drawingof the bore 155 and the portions 156, 152, and 158 of the rod 154 aredrawn out of proportion for clarity of description. As a practicalmatter, however, the dilference between the diameter of the reducedportion 157 and the diameter of the bore 155 is quite small and issuflicient to present considerable viscous friction or throttling to theflow of fluid. Extending from the central portion of the bore 155 is apassage 159 leading to the line 151. Also extending from the chamberformed by the piston 21, the bore 22, and the head 149 is a passage 161leading to a vertical passage 162 (see "FIG. 2) formed in the head andleading to the line 103.

Mounted on the forward surface of the apron 153 is a block 163 having athreaded bore through which extends a similarly threaded portion 164 ofthe rod 154. The rod is formed with a much larger threaded portion 165at its outer end, which threaded portion has a nut 166 mounted on it. Arod 167 is carried in the block 163 and extends into an aperture 168formed in the nut 166. Extending from the nut 166 is an indicator 169which is generally coextensive with a knob 171 which is fastened to anouter reduced portion 172 of the throttle rod 154. The knob 171 islocked in place by set screws 173 and 174 extending into the knob 171.

The apron 153 is formed with an aperture 175 which is much larger thanthe threaded portion 164 of the rod so that it does not interfere withmovement of the rod. A similar bore 176 extends through the abutment 145of the base 11 to permit free relative movement of the rod 154.

The operation of the apparatus will now be readily understood, in viewof the above description. The cycle of the machine is controlled by thesolenoid valves 47, -2, 69, 77, 85, 88, 94, 98, 113, 122, 127, 133, 138,96, and 102 which, in turn, are regulated by electrical controlsoperating on the coils of the solenoids. The electrical controlapparatus is of the conventional type and is well known in this art. Ata certain part of the cycle, it is necessary to withdraw the abrasivewheel from the bore in the workpiece. For that purpose, the TABLEcylinder is actuated and the abrasive wheel 19 is withdrawn from theworkpiece and moves axially. Before the wheel passes over a diamond fordressing, the table 12 carrying the abrasive wheel 19 is movedtransversely into backoff position. The 500 p.s.i. pressure output ofthe valve 105 passes through the line 108 and the checkvalve 110 andthrough the line 97 and the solenoid valve 98. This fluid pressureoperates on the cylinder 23 and moves the table forwardly (to the rightin FIG. 1) which moves the wheel 19 away from the surface of theworkpiece into a backoff position at which time it moves axially andmoves past the diamond and dressing takes place. The backotf position islocated so that the diamond removes the slight amount of surface fromthe abrasive wheel. The wheel moves longitudinally outwardly to the endof its retracted position and the TABLE cylinder 20 is reversed by meansof the TABLE INDEX valve 52. The abrasive wheel 19 returns along thesame path toward the workpiece bore 17. The oil passing through the line92 to the cylinder 22 for the grinding operation is shut on and off bythe solenoid valve 85. However, the particular pressure involved isdetermined by the pressure regulating valves 82 and 83 in the usualmanner to provide a. pre-determined oil pressure in the cylinder duringfeeding. When feeding takes place, oil is pressed from the other end ofthe cylinder. Since the valve 102 is closed, the oil is forced to flowthrough the throttle 152. This throttle is made up of the portions ofthe throttle rod 154 and the bore and, of course, is adjustable. Thevalve 102 is hydraulically operated and this operation is determined bythe valve 113. Oil which is pressed out of the cylinder chamber throughthe throttle 152 by the movement of the piston passes through the valve113 and goes to the drain line 4 2 through the valve 98. When it isdesirable to move the wheel 19 away from the workpiece surface fordressing or for loading of a workpiece or the like, it is only necessaryto operate the valve 113 to remove the pressure oil from the hydraulicactuator portion of the valve 102 and to connect that portion to drain.Then, the valve opens and oil is admitted to the forward end of thecylinder 22. It enters the cylinder through the passage 161. The oilwhich is delivered to the passage 161 through the line 103 in this stageof the operation originates in the line 41.

It can be seen then that, during the grinding operation, while the wheel19 is being pressed into the surface of the workpiece by the oiloriginating in the line 92, oil is being pressed out of the other end ofthe cylinder and its only means of escape is through the line 151 andthe throttle 152. The throttle is set to very accurate adjust ment forregulating the resistance to flow. Now, the table 12 moves relative tothe base 11 on friction-free guides, as is the usual method, so thatvery accurate determination of pressure in the line 22 results in veryaccurate determination of the pressure between the wheel 19 and theworkpiece 16. This is in accordance with the so-called controlled-forcemethod of grinding. However, it has been found in the past that thisarrangement in itself can result in somewhat erratic feeding of thewheel into the workpiece surface. This is possibly caused by vibration;the system is a friction-free sliding system with a spring in the formof the spindle on which the wheel is mounted. Such a system has a highdegree of resilience and a low amount of damping and lends itself tovibration. Vibration of extremely large displacement may take place,particularly when there is introduced into the system an impulse closeto its natural frequency as would be true in rounding up a bore. Also,there is a tendency in sliding guides to produce a stick-and-releaseaction in which sliding does not take place for a short period of timeand then, suddenly, a hydrodynamic film builds up and release of theholding takes place, so that the wheel jumps forwardly. Both of thesemotions is obviated by the present invention. The result of providing athrottle in the system in the manner suggested by the applicant is thata viscous resistance is introduced into the spring system. Any attemptfor the elements to move more rapidly than a predetermined speed willencounter extreme resistance because it is necessary for fluid to flowinto the chamber of the piston cylinder arrangement in order for suchaction to take place. This type of damping is time-oriented to preventsuddent movements between the elements. Since the valve 102 is closedduring feeding operation, the only way fluid can move in and out of thechamber is through the throttle 152. The throttle, therefore, has theeffect of damping any extraneous vibrations or erratic movements. Theadvantage of this viscous damping is that the amount of resistance isproportional to velocity, so that extreme variations of table movementwill result in large compensating resistance to such movement.

The engagement of the threaded portion 164 of the block 163 results inadvance and retraction of the rod and in adjustment of the passagebetween the rod and the bore 155 in the head 149. The rotation of therod to produce this adjustment is produced by rotating the knob 171.Now, the rotation of the rod also cooperates through the rod 167 and thenut 166 to advance or retract the nut 166 relative to the knob 171. Thefinely-threaded portion 164 and the coarsely-threaded portion ,165provide 7 a differential movement, permitting very accurate adjustment.Since the indicator 169 and the surface of the knob 171 are providedwith indicia, this results in the production of a micrometer indicatorwhich can be calibrated to show various settings of the throttle 152and, possibly, be calibrated in terms of rate of flow of fluid.

To thoroughly understand the advantages of the present invention, it isnecessary to review the art of controlled force grinding. To begin with,practice has proven that internal controlled force grinding leads thefield in obtaining the most work and economy from an abrasive wheel.Grinding machine users and builders continue to find new benefits andcapabiilties for improving production and quality with thisrevolutionary grinding method. One of the more common internal grindingoperations is that of precision finishing the track of a ball bearingouter race. The size tolerances and geometrical shape requirementsprovide grinding machine designers with one of their most challengingproblems. For example, the cross track curvature must not vary from atrue radius by more than .000020 to .000040 of an inch and a .0001 to.0002 size envelope must be maintained. This has to be accomplished withstock removal conditions that can change .025" piece to piece andworkholding locating surface dimension variations that actually exceedthat of the ball track tolerance requirements.

The machine system devices involved in this grinding process are: thegrinding machine with its wheel dressing device, the coolant and, ofcourse, the grinding wheel. a

In the past, with rate feed mechanism it was customary, whilemaintaining this degree of quality, to grind from 200 to 300 parts withone wheel in the 6 to 8000 s.f.p.m. The wheel then had to be changed. Insome cases, it could be used again on subsequent operations with smallerbores, but more often, the wheel had served its purpose and had to bethrown away. Today, using the controlled force internal grinding systemtogether with multi-wheel quill arrangements, never before possible withfeed rate grinding, the same wheel can produce ten times as manyworkpieces with improved quality. Controlled force internal grinding hasproven that a vitrified abrasive wheel is a tool with capabilities farexceeding the work to which it is currently being applied and that thecontrolled force grinding system is a way to obtain many additionalbenefits.

To review the controlled force grinding system, a common nomenclaturemust be established. Prior to 1963, all grinding machines, both internaland external, were built with feed rate infeed devices. That is, thegrinding wheel was advanced into the workpiece at a preset rate whichinvolved much art or guess work. On automatic machines, it was anestimate of stock variation, the grade wheel available and the type ofcoolant to be used that determined the rate setting. The grindingmachines went through the motions of a given cycle in exactly the sametime, but as inspection proves, not all the workpieces came out of themachines to the same size or finish. When this dilemma was recognized aslimiting the precision capabilities of feed rate grinding, particularlyon internal grinding machines, thoughts could be channeled into thedevelopments of a new grinding system. The outcome of much engineeringeffort, time and dollars, was the controlled force grinding systemapplied to an internal grinding machine.

The first consideration when comparing grinding systems is the forcebetween the work and the wheel. Laboratory tests prove that there is aparticular force with a given workpiece, coolant and grinding wheelcombination where the fastest stock removal will take place withoutdamaging the wheel. This is true with both external and internalgrinding. With internal grinding and the wheel mounted on a cantileverbeam, there is an additional problem. As the force between the work andthe wheel changes, so does the deflection of the quill. This, of course,causes changes in size and taper. Even with sparkout, in-process gagingand other cycle accessories, there is a limit to the 'precision that canbe obtained. In the simplest terms, with the controlled force grindingsystem, the pressure between the work and the wheel is preset to suitknown conditions that prevail. The rough grind cycle time will varysomewhat with significant changes in stock conditions, but the workpiecesize and conditions of the wheel for grinding action Will remainconstant.

In most instances a new machine with advanced capabilities means moresophistication. However, this is not true with the automatic internalcontrolled force grinder shown in the present case, where a simplehydrostatic way system and a hydraulic force piston provide the basicfeed mechanism; this replaces the old complex feed box and lead screw.

Any controlled force feed slide must be frictionless. In technicalterms, Coulomb friction must be eliminated. Since a controlled forcefeed slide is not anchored to a screw, it is free to move backward aswell as forward in the feed direction. Here, an apparent road block inthe design concept of. a controlled force grinding machine has been usedto great advantage. By providing a hydraulic damper with controllableshock absorbing characteristics in the hydraulic force feed system, acontrolled force machine can be adjusted to provide the fastest possible'rounding up of the eccentric surface conditions of the usual roughworkpiece. In effect, when the wheel first contacts the work, it willcontact the high spots of an irregular surface with more force than onthe low zones. For example, this allows an out of round rough bore to berounded up, with the entire surface clean ground, much earlier in thecycle than would be possible with a feed rate grinding system. Thiscomplements the ability of maintaining a more precise amount offinishing stock just prior to final size.

Now let us consider the grinding force control in a little more detail.When we talk about controlled force, it is in relative terms. Just asthere is not a pure feed rate, there is also not a pure controlledforce. We have a force-rate spectrum as shown in FIG. 8. Controlledforce is closer to the pure force end of the spectrum and controlledrate closer to the pure rate end of the spectrum.

Due to the required viscous damping in the controlled force slide asdescribed before, the grinding force will decrease with increasedgrinding rate. This is very desirable, since it will regulate thegrinding process. When the penetration rate of the wheel decreases, dueto dulling, the force between wheel and will slowly build up causing thewheel to self-sharpen, which in turn, makes the wheel cut faster. Againthe regulating process takes over. The faster grinding rate due to ratesensitive damping causes the force between wheel and work to reduceslowly, which prevents loading of the wheel, burning, and high micro.

However, with controlled force, the change in the force of the wheelagainst the work is more subtle and smaller than with feed rate. It islimited to a maximum force which is preselected for a given wheel andlength of part such that the wheel will self dress when the penetrationrate slows down due to dulling and continues cutting with its highestefficiency. On a controlled force machine with the input forcepreselected at, say, lbs., the force of the wheel against the workcannot exceed 150 lbs., whereas, on a feed rate machine due to themechanical advantage, forces of 1,000 lbs. and more can develop, thusdamaging wheels, quills, and bearings.

Controlled force grinding normally requires that the wheel be as wide asthe work surface to be ground. However, with high damper strength and afeed stop control, long bores can be ground with narrow wheels.

The controlled force grinding system with its advanced capabilitiesoffered opportunities to develop new control devices to get even greaterprecision for size holding, finish and geometry with a completelyautomatic cycle. These controls complement the cutting action of thewheel and the finish potential as well.

During the life of an internal grinding wheel, for instance, it becomessmaller in diameter with each subsequent dress, and this changes thegrinding conditions. As the wheel D. is reduced, the surface speedchanges, the wheel-work contact area is reduced. This, in turn, resultsin a gradually increasing RMS finish. A retracting stop in the crossslide unit is frequently used to monitor the final .001 of stock removalto insure that, just prior to finish size, a given wheel will be cuttingunder exactly the same conditions regardless of wheel size and thusinsure greater finish consistency. This escapement rate feed, at thelast instant of the 1D. grinding cycle, is adjustable and can be set tosuit a given machine setup. This retracting stop is really another forceregulating mechanism. It reduces the applied force even further than thedamper, or can stop the slide entirely for final sparkout. In otherterms, the retracting stop acts as a force divider. The input forceminus the force against the retracting stop is equal to the wheel forceagainst the work.

To review again, the controlled force grinding system gives the bestwheel/coolant grinding performance without wheel damage for variablestock removal conditions. The retracting stop provides additionalcontrol for low finish requirements as the wheel size changes.

At the present time, there is much development work with high wheelsurface speeds. High speed grinding tends to produce heat which, if notcontrolled, will cause workpiece surface damage. The controlled forcegrinding system complements high speed grinding by being able to provideoptimum forces. In many cases, significantly faster cycles can beobtained without damaging the wheel or burning the work surface.

Adaptive controls are also a part of the controlled force equipment.When specifications demand the ultimate in short cycle time, aboveaverage geometrical requirements or rough stock conditions are presentthat hinder the grinding process, machine component operationalvariations can be monitored and signals fed back to make desirable cyclechanges automatically.

A typical control system for maintaining a low micro finish and accuratesize is the so-called automatic drift control. Here the machineconstantly senses the amount of finish stock and the time required forthe final grind. The length of finish grind is affected by diamond wearor thermal changes in the machine. If the finishing time becomes short,lets say due to diamond wear, the micro could exceed the specifiedtolerance. However, if the finish time becomes too long, the finishwould have a low micro reading, the cycle time would be longer. Certainlimits for the amount and time for the finish portion of a cycle arepre-set. When the machine senses a change from this reference, it willautomatically adjust for diamond wear and the effects of thermal drift.This maintains constant finish grind parameters.

Ammeter monitoring of the wheel drive motor is a common adaptive controland can be used on controlled force machines. It can give an electricalsignal to control the final portion of a cycle in terms of finish andtaper relative to the current load (e.g. in long bores on internalgrinders).

Machine cycle combinations with controlled force grinding are numerousand different from feed rate cycles. The controlled force slide in feedrate is, of course, determined by the force at which a particular wheelwith a given coolant can grind into the workpiece material. The bestforce to use is easily determined. This is accomplished quickly bystarting with a conservative pressure setting and recording the timenecessary for a particular wheel to remove a given amount of material.The force can then be increased in convenient increments until anincrease in force does not produce a reduction in time. When the properforce is determined, then appropri- 10 ate cycles can be developed foreither single or multiple wheel applications.

The most common cycle is the so-called interrupt for dress. Frequently,because of pure controlled force performance or the ability to useseveral wheels on a single quill, as a side benefit of controlled force,dress at load cycles can be used. This type of time saving cycle mightnot have been possible with feed rate grinding.

Other cycle comparisons include skip dressing and multi dressing. Skipdressing has always been used with feed rate internal grinding for ballbearing ball tracks in outer races. The controlled force system cangenerally skip twice as many cycles as the feed rate system before adress is necessary on this type of work.

Without adding sophisticated and costly controls to a feed mechanism,the basic controlled force system allows for an unlimited number ofinterruptions for dress which are necessary for grinding modern exoticmaterials.

Multi wheel applications with controlled force gives one of the newestand most interesting cycle innovations. The best possible wheel gradeand force can be determined for roughing with an equivalent selectionfor finishing. No longer is a compromise wheel grade selection necessaryto complement two objectives. Most of the time on feed rate grinders,the finish requirements dictated the wheel grade and cycle at theexpense of the stock removal ability. The newest application ofcontrolled foced multiwheel grinding is true abrasive machining.

Several controlled force machines are now in production which grind thecomplete internal contour of a bearing outer race from a solid blankbushing. A #210 ball bearing outer race with an CD. of 3 /2 and a widthof can be form ground in one chuckling, removing half a cubic inch of52100 steel in approximately one minute. This single operation replacessix separate I.D. grinding operations previously used. It produces afinished ball track, a rib diameter, two chamfers plus a tapered surfaceadjacent to the (angular contact) ball track. With a two wheel quill, adriven diamond wheel dresser forms the contour on the outboard wheel,and a radius dress provides the geometry on the second ball trackfinishing wheel. The ball raceway is semi-finished -by the first wheel.Oil coolant is required on this type of abrasive machining.

FIGS. 6 and 7 illustrate how the viscous throttling used in the presentinvention is helpful in controlled force grinding. The force arrows aredrawn to indicate their relative sizes under various conditions. Theequation F,, ,.=F indicates that the total force, F available due to oilpressure in the cylinder is divided between the grinding force, F andthe force F absorbed by the resistance to flow of the fluid through thethrottle. When the wheel is new and is large compared to the bore, asshown in FIG. 6, the piston is allowed to move slowly, due to theadvance of the wheel in grinding its way into the surface of theworkpiece. After a large number of workpieces have been ground in theautomatic grinding machine, the diameter of the wheel is reduced in sizeby wear and by dressing, as shown in FIG. 7, so that it is relativelymuch smaller than the bore. It then cuts much more rapidly and, if thegrinding force, F were to remain the same, the qualities of the finishedworkpiece would suffer. For one thing, the rate of movement of theabrasive wheel into the workpiece material would increase substantially,resulting in a deterioration in the fineness of surface finish. With thepresent invention, however, the start of such a rapid movement isimmediately counteracted by a similar increase in the viscous force, F,,with an attendant decrease in the grinding force, F The decrease ingrinding force will slow down the progress of the wheel through theworkpiece material, thus restoring most grinding parameters to theconditions prevailing at set-up time (FIG. 6).

Another situation that arises frequently in automatic grinding machineshas to do with wheel dulling. As grinding progresses (between dresses),the wheel becomes duller. In a feed-rate machine, when the wheel getsduller, it is pressed onward into the material, nevertheless, so thatthe force increases greatly; eventually, the surface of the wheel breaksdown under this great pressure, new grains of abrasive are exposed, andgrinding begins to speed up. In the past, this automatic dressing ofdull wheels was not available in controlled force machines, because theforce could not go up when the wheel became dull.

With the present invention, however, when the wheel becomes dull, therate of grinding decreases, and the velocity of the wheelhead table alsodecreases. With the viscous damping, the decrease in table velocitymeans less resistance to fluid flow and a decrease in F Thus, more forcefrom F is available for grinding (F this increase in F causes the wheelsurface to break down, exposing new grains of abrasive, and speeding upthe grinding process again. This returns the grinding parameters totheir original values and helps to maintain the quality of the finishedworkpiece surface to the original predetermined values.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come Within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. A grinding machine, comprising (a) a base,

(b) a workpiece support mounted on the base,

(c) a Wheelhead support adapted to carry a grinding wheel and mounted onthe base,

((1) a hydraulic actuator having a piston movable Within the actuatorconnected to one of the supports for bringing about relative feeding andretractive movement between the workpiece support and the wheel headsupport,

(e) means for presenting an incompressible fluid to the actuator at oneside of the piston at a controlled pressure during feeding movement, theactuator consisting of a cylinder having a head at the other side of thepiston, the head being provided with a passage, and a damper rod lyingin the passage accessible from the exterior of the machine to permitregulation of the relative positions of the rod and passage 12 and,therefore, regulation of the restriction to flow of fluid presentedthereby,

(f) means connected to the actuator at the said other side of the pistonto permit escape of fluid at a restricted selected rate during feedingmovement and alternatively to present a fixed pressure fluid during theretractive movement, and

(g) separate sources from which originate the controlled pressure fluidand the fixed pressure fluid.

2. A grinding machine as recited in claim 1, wherein the last-namedmeans consists of an adjustable restriction and a valve connected inparallel with each other, the restriction and the valve being connectedon one side to the actuator and at the other side to a selector valvewhich is, in turn, connected to a source of pressure fluid and a sump.

3. A grinding machine, comprising (a) a controlled force feed mechanism,

(b) a source of controlled pressure fluid connected to a first portionof the mechanism during feed movement, A I

(c) an adjustable flow restrictor connecting a second portion of themechanism to a return line during feed movement,

(d) a source of fixed pressure fluid connected by a path independent ofthe restrictor to the second portion of the mechanism during retractionmovement, and

(e) means connecting the first portion of the mechanism to a return lineduring retraction movement, the restrictor presenting viscous resistanceto the flow of fluid during the feed movement, so that the totalresistance to movement provided by the restrictor is proportional to thevelocity of movement.

References Cited UNITED STATES PATENTS 1,920,228 8/1933 Wood 51165.045X1,932,760 10 /1933 West 51--165.03UX 2,680,941 6/1954- Hahn 51-50HX2,475,326 7/1949 Johnson 91-47X 1,822,667 9/1931 Proell 91-47X JAMES L.JONES, IR., Primary Examiner US. Cl. X.R. 51-165

